Proportional spacing display apparatus

Abstract

A proportional spacing display apparatus for displaying characters on a display screen with spacings corresponding to types of character. One character display cycle comprises a half cycle for reading character data from a video memory and a half cycle for rewriting the character data in the video memory. The character data reading half cycle has a fixed time period necessary for data reading, while the character data rewriting half cycle has a time period variable with character widths.

What is claimed is: 
     
       1. In a display apparatus with a proportional spacing control device for displaying characters with spacing corresponding to the types of character, comprising: data memory means for storing character data;   character data reading means for reading the character data from said data memory means for display;   data rewriting means for rewriting the character data stored in said data memory means;   control means for allocating a character display cycle including a fixed character data reading period for reading by said character data reading means and a variable character data rewriting period in accordance with a width of the character to be displayed; and   display means for displaying a character which is read by said character reading means during one character display cycle corresponding to a sum of the character data reading period and the character data rewriting period determined by said control means.   
     
     
       2. A display apparatus as claimed in claim 1, wherein the data rewriting is effected during the data rewriting period having the variable time period in accordance with the widths of the characters only when the time period is sufficiently long for providing access and there is an access request from said rewriting means. 
     
     
       3. In a computerized word processor having a display for use with an editing function and a printer capable of printing characters of variable width, the video display being driven in correlation with a CPU timing cycle which permits data reading and writing to a storage medium which can be addressed for display of characters with proportional spacing equivalent to the proportional spacing of the printed characters, the improvement comprising: means for providing a character clock signal having a pulse width that is proportional to the width of the character to enable a character display;   means for adjusting the pulse width during a CPU timing cycle, and   means for compensating for a shortened data reading and writing time period of a narrow character width during the display cycle of a wider character.   
     
     
       4. The invention of claim 3 further including a constant frequency clock pulse generator connected to the means for adjusting the pulse width. 
     
     
       5. The invention of claim 4 wherein the means for adjusting the pulse width includes a first and second counter and a flip flop, the first counter counting the clock pulses equivalent to a character width and the second counter counting a predetermined number of pulses when the flip flop is set by the first counter. 
     
     
       6. In a display apparatus with a proportional spacing control device for displaying characters with spacing corresponding to types of character, comprising: a character memory for storing character codes of character to be displayed;   an address counter for providing an address signal to said character memory;   reading means for reading the character code stored in the address indicated by the address counter from the character memory;   dot clock pulse generating means for generating dot clock pulses having a fixed cycle;   character generator for generating dot pattern data in accordance with the character code read by said reading means and for providing the dot pattern data to a display screen in synchronizing with the dot clock pulses to display the characters; and   character pulse generating means for generating character pulses having pulse intervals variable with character widths and for providing the character pulses to the address counter, thereby to effect address renewals of the address counter in accordance with the character width, said pulse interval including a fixed period required for said reading means to make access to said character memory for reading the character data from said character memory and a variable period in accordance with widths of the characters.   
     
     
       7. A display apparatus as claimed in claim 6, further comprising rewriting means for rewriting the character data stored in said character memory during said variable period only when the time period is sufficiently long for providing of access to said character memory for the rewriting operation.